The present invention relates to electric power devices, and more particularly, but not exclusively, relates to circuitry to provide electric power from radioactive decay and/or other nuclear processes. One nonlimiting embodiment of the present invention is directed to a radioisotope-based battery; however, in other embodiments different applications are envisioned.
Radioisotopic power sources have been used for space exploration for over 40 years, and have played major roles in high profile space missions such as the Apollo Lunar landing and the Cassini-Huygens mission exploring Saturn and Titan. Typically radioisotopic nuclear power is used in two forms: radioisotope thermoelectric generators (RTG) and radioisotope heater units (RHU). Both of these applications involve the conversion of nuclear radiation energy first into heat, which typically results in low conversion efficiency if the thermal energy is ultimately intended to be converted into electricity. Specifically, efficiency is limited by the Carnot cycle limit, among other things.
Such limits can be extremely severe for a space-based power system because a high-quality heat-sink is difficult to provide in spacecraft. Under such circumstances, generally the best approach is a large surface-area space radiator for which the heat ejection capacity is constrained by the black body radiation limit. Further compounding the problem is the low Z coefficient of available thermoelectric materials. As a result a typical space-based RTG operates at a very low efficiency of about five percent (˜5%).
The situation is little better for thermionic converters. Under certain conditions, thermionic conversion can achieve about ten percent (˜10% ) efficiency. Unfortunately, such circumstances usually are degraded in space, which results in lower performance. As reported for the Russian TOPAZ-II, about 5.2% efficiency was obtained with this type of device. See, G.L. Kulcinski, “History of Soviet Topaz Reactors”, http://fti.neep.wisc.edu/neep602/SPRING00/lecture35.pdf.
Radioisotope power systems continue to be used in space, such as the Jupiter Icy Moons Orbiter (JIMO) mission. To approach conversion efficiency greater than the thermal-based systems, new techniques are needed. Some attempts to address this need include dynamic (DIPS) systems such as Sterling engines and alkaline metal thermal (AMTEC) converters. U.S. Pat. No. 3,931,564 is directed to yet another type of radioisotope energy converter. However, each of these attempts faces various developmental issues that have yet to be resolved. As a result, further contributions to this area of technology are desired.